Electrophysiology catheters are commonly used for mapping electrical activity in the heart. Various electrode designs are known for different purposes. Certain types of electrical activity within a heart chamber are not cyclical. Instead of regular, coordinated electrical activity, disorganized electrical signals may impede heart function. Such electrical activity is random from beat to beat. An example is atrial fibrillation, which results from improper control of the timing and sequence of muscle contractions associated with a heartbeat. Other examples include arterial flutter or arterial fibrillation, and ventricular tachycardia originating in scars in the wall of the ventricle that have resulted from infarcts.
Suitable treatments may include performing an ablation procedure, such as targeted ablation of myocardial tissue to treat the cardiac arrhythmias. One specific type of an ablation procedure is termed pulmonary vein isolation, in which tissue in the area adjacent the junction of the pulmonary veins and the left atrium is ablated. In such treatments, to reduce fibrillation or other arrhythmias, radiofrequency energy may be delivered by an ablation electrode to pulmonary vein tissue in order to create one or more lesions to block electrical conduction and to electrically isolate certain areas. This isolation may minimize the migration of irregular electrical activity to other areas of the heart. To deliver the radiofrequency energy to ablate tissue and thereby form conduction blocking lesions one or more ablation electrodes may be brought into contact or close proximity with atrial and pulmonary vein tissue.
A catheter may be used to position the ablation electrode to apply RF energy and create a lesion to break arrhythmogenic current paths in the cardiac tissue. It is desirable to know the temperature of the ablation electrode to prevent heating the tissue excessively. Current ablation electrodes may be equipped with thermocouples, but due to the size of current thermocouples in relation to the catheter and ablation electrode the thermocouple is usually attached at an edge of the ablation electrode (also “ring electrode”) rather than at a central (or “focal”) band of the electrode. The temperature at the edge of an ablation electrode may be significantly different from the temperature at the central band. Furthermore, and particularly when the ablation electrode is positioned correctly, the edge of the ablation electrode may be less likely to be in contact with the tissue being ablated. A temperature difference may also be accentuated in longer (e.g., 8 mm) ablation electrodes. For these and other applications, it would be desirable to determine the temperature of an ablation electrode at the point of contact with tissue as accurately as possible to avoid excess heating, or even charring, of the tissue. Accordingly, the embodiments of this disclosure as described in the following materials satisfy these and other needs.